How to find the value of coefficient!?!?!

I need help with this question.
A block of unknown mass is placed on a hinged incline plane with an adjustable angle of elevation O (theta).  Initially the incline plan is level and the block is placed on the plane with its front face 1.00m from the hinged end.  It is desired to determine the static coefficient of friction Us (coefficient) between the block and the incline plane.  This is done by slowly increasing the angel O theta until a critical angle O theta c (critical) is reached at which the block begins to slide.  The critical angle is measured at 36.9 what is the value of Us (coefficient) .   How do I solve this?!
Thanks for your time